A NOVEL SYNTHETIC ROUTE TO RIGID-ROD POLYIMIDES

A new synthetic approach to soluble, rigid-rod, aromatic polyimides is described. The polycondensation is done by a Pd-catalyzed aryl-aryl coupling of N,N'-bis(4-bromo-2,5-didodecyl-phenyl)-1,2:4,5-pyromellitic diimide (2) and 2,5-didodecyl-1,4-benzenediboronic acid (3). Here, the imide structure is already preformed in monomer 2. A structurally identical polymer is synthesized by the classical procedure condensing 1,2:4,5-pyromellitic dianhydride (PMDA) (4) and 4,4''-diamino-2,5,2',5',2",5''-hexadodecyl-p-terphenyl (5). Both polymers are characterized in detail by H-1 and C-13 NMR spectroscopy, membrane osmometry and size exclusion chromatography. The average degree of polycondensation is of the order of 15. The thermal behaviour of the polymers is studied by differential scanning calorimetry and thermogravimetrical analysis.